1. Field of the Invention
This invention relates generally to the detection of the products of combustion and, more particularly, to the detection of the toxic gaseous products of combustion.
2. Description of the Related Art
In recent years, publicity has been given to devices which indicate the presence of combustion. These devices have been and are being widely deployed in private and commercial buildings to alert residences of a potentially dangerous situation. In order to insure that the devices are operational, a requirement has been imposed that devices must be capable of being tested, in situ, to insure availability when needed.
In a sense, the information provided with respect to the solid particle detectors of particles of combustion has been deceptive. The detectors generally referred to as smoke detectors are, in fact, solid particle detectors. The mechanisms upon which the solid particle detectors operate are typically radiation induced or photo-induced conduction. When particulate matter is introduced into the chamber of the solid particle detector, the particulate matter causes ionization of the air in the chamber. The ionization of the air causes a decrease in voltage in the sensing chamber, the decrease in voltage, when sufficiently large, resulting in activation of an alarm device.
The solid particle detectors suffer from two major disadvantages. First, the material detected is typically more prevalent when active and complete combustion is taking place, and not during a smoldering stage (i.e., with incomplete combustion). Second, the principal harmful ingredient from complete or incomplete combustion is carbon monoxide, a gas which is not detected by the solid particle ionization or photo-electric detectors. In the test procedure of these devices, the voltage across the chamber is lowered (without becoming zero) to determine if the alarm device is activated when voltage is decreased a predetermined amount.
Recently, a true smoke detector, identified as the Figaro Gas Sensor TGS 813 or the improved TGS 203 (having two heater elements to increase the sensitivity to carbon monoxide) has been distributed in the United States by the Figaro USA, INC of Wilmette, Ill. This device is filling the need for a device that is able to detect gases and, more particularly, to detect carbon monoxide. The sensor element of the smoke detector is comprised of a sintered bulk semiconductor consisting principally of tin oxide (SnO.sub.2). When an appropriate gas is introduced into the smoke detector, the resistance across the smoke detector falls. However, the smoke detector unit has not been provided with the test circuits that would permit on location testing, the test circuits that would make the unit acceptable by Underwriters Laboratory requirements for widespread (including residential) applications.
A need has therefore been felt for apparatus and an associated method which simulate the introduction of an appropriate gas into the smoke sensor to determine if the test circuits, including an associated alarm device, are functional.